Enzymatic hydrolysis of old corrugated cardboard (OCC) fines from recycled linerboard mill waste rejects

Abstract

A significant fraction of short fibers (fines) is produced while recycling Old Corrugated Containerboards (OCC), which are usually rejected as solid waste stream, requiring landfilling and posing environmental problems. The major component of these fines rejects are primarily cellulose that can be hydrolyzed into sugars for possible fermentation into biofuels, bioplastics or other sugar based products. Use of fines also offers benefits such as negative costs and production of fermentable sugars without requiring complex pretreatment processes, now required to hydrolyze and eliminate inhibitors from hydrolyzate. Enzymatic hydrolysis of reject fines from a recycled OCC mill, employing different strains of cellulases, were investigated. Fillers (up to 30 mass %) in the fines increases the required dosage of enzymes and costs. Enzyme loading can be lowered by addition of surfactants to reduce their inhibitory activity. The nonionic surfactant Triton X-80 improved hydrolysis yields by up to 10 percent points.

Description

CROSS REFERENCE TO RELATED APPLICATION

The present application is a non-provisional of, and claims priority from, U.S. Provisional Patent Application No. 61/953,152, filed Mar. 14, 2014, the entirety of which is expressly incorporated herein by reference.

FIELD OF THE INVENTION

This invention relates to processing of cellulosic solid waste from paper related industries for extraction of fermentable sugars.

BACKGROUND OF THE INVENTION

Rising oil prices, unstable supply and the demand for sustainable environmental friendly energy sources has increase the interest in research and development of bio-energy sources such as bio-ethanol. Carbohydrates are a natural resource commonly available as lignocellulosic biomass that can be hydrolyzed into sugars to be further converted via fermentative or thermochemical processes into useful products [1]. Among the important products that can be derived are ethanol (cellulosic), butanol and similar advanced fuels, platform chemicals such as acetone, furfural, levulinic acid, gamma valerolactone and bioplastics such as polyhydroxy butyrates or valerates [1-3]. These products are a substitute for fossil fuels or starch based carbohydrates, thus providing an alternate sustainable resource. The plastics are biodegradable and thus are beneficial to the environment in comparison to petrochemicals and their derivatives [4]. Cellulosic biomass is a promising material for bio-energy that avoids the usage of corn and other food grains and thus avoids the necessity of competing with edible sugars.

One of the biggest markets using cellulosic biomass is the pulp and paper industry. The global production of paper and paperboard was 403 million tons in 2011. This amount is about 30% of the industrial round-wood. The recycling rate of paper has been gradually increasing from 50% in 2007 to 53% in 2011. North America now has the highest recovery rate (64% in 2011), followed by Europe (58%) and the Asia-Pacific region (48%) [5]. This process of recycling pulp and papers is to reduce cost and to have a sustainable environmental policy. [6-8].

Repeated recycling of pulp decreases the length of fibers which become shorter and stiffer, losing their ability to bond within the paper sheet. At a certain stage, their net contribution to the sheet becomes negative and they need to be rejected. These short fibers known as fines are recovered from the wastewater stream and typically sent to landfills. The solid residue can also be applied for land use or animal bedding [9-12]. However, the fines can be a very useful resource for sugar production because they are predominantly composed of cellulose which could be converted into glucose and other monomeric sugars. Currently, some paper companies pay $25 to $80/(wet) ton for disposal of the fines [9, 13, 14]. Besides their cost advantage, the supply of fines from paper mills is fairly homogeneous and thus there is minimal influence of seasonal or weather related supply challenges compared to other agricultural biomass [6, 8].

A number of different processes including incineration, gasification and pyrolysis may be used for treating this waste fines stream [10]. However, given their energy consumption and complex processes, direct hydrolysis of the cellulose into sugars can be particularly attractive due to the simplicity of the process and ready use of the sugar solution after concentration [15]. These sugars can be used as a feedstock for conversions into biofuels and bioplastics such as polyhydroxy alkanoates or into platform chemicals such as succinic acid, lactic acid, levulinic acid and furfurals [1, 16-18].

Of the varieties of papermill fines rejects, those from recycled pulp mills using old corrugated cartons are particularly important. Some modern OCC mills find that rejecting ‘inactive’ fines into the waste stream can be more profitable than using them in the manufactured product, particularly recycled linerboard. The reject stream thus contains higher cellulosic fines contents and typically lower minerals than deinked pulp rejects in the waste streams of fine papers or tissue mills.

Lignocellulosic materials are excellent sources for energy products, platform chemicals and bioplastics. Sugars produced by the degradation of carbohydrate polymers can be fermented into ethanol and butanol as energy sources. Sugars and cellulose degradation compounds can serve as platform chemicals in the production of bulk chemicals and they can also be used as feedstocks for microbial production of plastics such as polyhydroxy alkanoates (PHA).

The waste stream from recycled paper mills contains cellulosic fines and also particles of mineral origin, typically clay or calcium carbonate from the fillers and coatings used in the waste paper. The cellulosic fines are easily hydrolyzable by either acid or enzymatic processes. In the enzymatic process, a cocktail of cellulose enzymes acts progressively and sequentially to open up the cellulose crystalline structure and depolymerize it, producing monomeric sugars. The sugars are primarily glucose and certain other common hexoses which are fermentable into ethanol, butanol or other products, leading to bioplastics such as polyhydroxy alkanoates (PHA).

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Each of the foregoing references is expressly incorporated herein by reference in its entirety.

SUMMARY OF THE INVENTION

The present technology study focuses on the enzymatic hydrolysis of OCC fines rejects from a recycled linerboard mill. The saccharification of this waste stream to yield fermentable sugars was identified and optimized using different commercially available enzyme mixtures. The effect of enzyme activity (characterized by their FPUs), impact of hydrolysis temperature, pH, pulp type, filler composition were investigated. Furthermore, methods of enhancing the enzyme activity and sugar yields by binding the minerals using different surfactants (cationic and nonionic) were also investigated.

A significant fraction of short fibers commonly called as fines is produced while recycling OCC (Old Corrugated Containerboards). These fines are usually rejected as solid waste stream that further requires landfilling and poses environmental problems. The major component of these fines rejects are primarily cellulose that can be hydrolyzed into sugars for possible fermentation into biofuels, bioplastics or other sugar based products.

In addition to environmental advantages, use of these fines also offers benefits such as negative costs and production of fermentable sugars without requiring any complex pretreatment processes that are required to hydrolyze and eliminate inhibitors from hydrolyzate.

According to the present technology, enzymatic hydrolysis of reject fines from a recycled OCC mill was performed. Different strains of cellulases were tested for their compatibility and Trichoderma Reesei was found to be the most effective at loading levels of 5-50 FPU (/g of oven dry mass). A maximum hydrolysis yield of 43% sugar (g/g-OD fines) with 50 FPU was observed. See, Byeong Cheol Min, Bhavin V. Bhayani, Bandaru V. Ramarao, “Enzymatic Hydrolysis of Old Corrugated Cardboard (OCC) Fines from Recycled Linerboard Mill Waste Rejects”, Proc. AICHE 2013 (Nov. 3-8), extended abstract P346631, expressly incorporated herein by reference.

The presence of fillers (up to 30% by mass) in the fines increases the required dosage of enzymes that increases the costs of hydrolysis.

It was found that the required enzyme loading can be lowered by addition of nonionic surfactants to reduce their inhibitory activity. The nonionic surfactant Triton X-80 improved hydrolysis yields by up to 10 percent points.

Paper mill rejected fines are a good source of biomass for sugar production given the low lignin content (Table 1), negative price, pre-processed nature which negates requirement of a pretreatment regime and the larger surface area and porous nature of the particles compared to other naturally occurring biomass. The particle size of about 3 μm is much smaller than typically milled biomass particles whose sizes are in the sub-millimeter ranges. The enzymatic hydrolysis yield of fines achieved was up to 70% of reducing sugars from fermentable sugars in the fines. The sugar yield of rejected fines is similar to the hydrolysis yield of woody biomass which was reported as 70% to 90% for lignocellulosic biomass [3, 19].

TABLE 1
Characteristics of fines of rejected sludge from OCC paper mill
Fines (rejected fines containing
fillers and contaminants)   Value
pH                          6.4
Solid content               0.52%
Particle size               2.1-3 μm
Zeta Potential              (−) 9 m V
Lignin                      3%
Ash content Analysis
Total                       33%
Calcium Carbonate           15%
Other fillers and residuals 18%

The commercialization of “waste cellulosic fiber” based sugar requires deactivation of inhibitory potential of contaminants and ash which includes fillers, calcium carbonate being one of the most powerful inhibitors [20]. Several surfactants were studied to improve enzymatic hydrolysis. Even though the precise mechanism and principle were not defined, many surfactant studies have concluded the feasibility of surfactant for advanced enzymatic hydrolysis [21-27]. Addition of non-ionic surfactant Tween-80 improved hydrolysis yield of mixture of UKP and CaCO₃ in various enzyme dosage (FIG. 6). The required enzyme dosage for complete hydrolysis (about 70% sugar conversion) was reduced from 50 FPU to 30 FPU for the fines (FIG. 7). Using the surfactant it was possible to minimize enzyme dosage for maximum hydrolysis yield which is important for economic sugar production.

The optimum dosage of surfactant was in range of up to 10%. Excessive dosage (above 10%) caused agglutination of substrates and thus a decreased hydrolysis yield. Other studies suggested similar dosage of surfactant for enzymatic hydrolysis [21, 24, 27]. Our research indicated a dosage of 7% for the synthetic fines mixed UKP and CaCO₃ (15%) but presented wide range of surfactant dosage (3 to 9%) for the fines. Application of pH 4 buffer instead of pH 5 buffer increased hydrolysis yield and decreased enzyme dosage for maximum hydrolysis yield (FIG. 8). The yield improvement of the combination method was more significant at the 10 FPU enzyme dosage. The demand of low pH buffer is regarded due to CaCO₃ in the fines. Adjusting pH is good for not only optimizing hydrolysis condition for enzyme but also dissolving calcium carbonate from fibers.

The presence of fillers and crystalline fibers are considered as primary inhibitors for the hydrolysis process while presence of other contaminants such as inks have a lesser inhibitory potential and thus can be classified as secondary inhibitors based upon their inhibitory activity. The process of drying fines is to be avoided for effective enzymatic hydrolysis. The enzymatic hydrolysis yield of both the fines and UKP was decreased by about 30% after drying (Table 2) which is due to decreased accessibility of micro-fibrils. To increase accessibility of cellulose, dissolving in alkaline method can be applied [28]. Beating method is also studied for recycled fiber to increase accessibility of cellulose by increasing swelling ability, water retention value, pore size and pore volume [29].

TABLE 2
Drying effect of materials on enzymatic
hydrolysis yield (replication n = 2).
	Hydrolysis yield (%, g/g)
25 FPU, 3 days	Non-dried	Dried	Dry Effect (%)
Fines	30.35 (±1.38)	21.41 (±2.1)	−29.5
Unbleached Kraft Pulp	92.11 (±0.8)	64.06 (±0.4)	−30.5

Even though enzyme dosage was reduced from 50 FPU to around 25 FPU for 1 g of fine maximum hydrolysis yield by combination process, 25 FPU is still high demand of enzyme and not profitable. The development of contaminants separation and surfactant injection is expected to make profitable enzyme dosage and high yield of sugar from fines.

The fines have a potential to produce sugars as a resource of biomass. The main inhibitor of enzymatic hydrolysis fines was CaCO₃ (15% of fines) which is decreasing enzyme activity by adsorption and increase of pH. Nonionic surfactant, 3-9% of Tween-80, improved enzymatic hydrolysis yield of paper industrial waste fines in addition of 50% increase at 10 FPU and reduced enzyme dosage of Trichoderma reesei ATCC 26921 for the maximum yield. The surfactant application was simple and an economical option to increase profitability and productivity of sugars from waste cellulosic fibers by improving enzyme activity. Using proper pH buffer for optima enzymatic hydrolysis condition pH 5 was also a considerable method for economical sugar production from fines. It was found that addition of surfactants and acid mitigated inhibitor effect of CaCO₃ which has a high inhibitory potential. Also, separation processes to reduce fillers and contaminants from fines is considered to save more enzymes.

The present technology processes a waste stream comprising cellulosic fines, e.g., from recycled packaging paper mills, into a stream of fermentable sugars. These may be fermented to yield bioethanol which is of value as a fuel, and/or manufacturers of other products such as bioplastics such as polyhydroxy alkanoates.

According to a preferred embodiment, a process is provided to:

(a) hydrolyze the cellulosic fines found in recycled paper mill waste streams using a commercially available cellulose enzyme formulation;

(b) increase the enzymatic hydrolysis yield by shielding the inert components of the waste stream using a surfactant; and

(c) optimize the surfactant with respect to its composition (anionic, non-ionic or cationic) and dosage.

The enzymes, however, may have a competitive binding affinity for inorganic particulates, resulting in a non-specific absorption of some or all types of enzymes to the particles. Indeed, similar high surface area particles are used in the purification of similar enzymes. Therefore, in the presence of inorganic particles, such as precipitated calcium chloride (PCC), the activity and bioavailability of the enzymes may be substantially reduced.

It has been found that surfactants are able to coat the inorganic particulates and otherwise reduce binding of the hydrolytic enzymes, leading to a significant increase in activity, thus saving cost and increasing efficiency. It has been found that effective surfactants do not also block binding or biological activity of the enzymes for the cellulosic particles and components of the solution.

Cationic, non-ionic and anionic surfactants were tested at various dosages. A non-ionic surfactant, Tween 80 (polysorbate 80) was better than the cationic and anionic surfactants.

The inorganic particles may be separated from the waste stream.

Some investigators have suggested the use of anaerobic fermentation as a means to degrade the organic components in the waste stream, but due to presence of large amount of calcium carbonate, kaolin and other fillers, they give rise to problems such as scaling of biomass, reactors and pipes, reduced specific methanogenic activity and loss of buffer capacity, and essential nutrients for anaerobic degradation.

Commercially available hydrolysis enzymes include Cellic® HTec3, a concentrated hemicellulase that works alone or in combination with Cellic® CTec3 cellulase enzyme from Novozymes (Denmark).

See:

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Khodaverdi, Mandi, et al. “Kinetic modeling of rapid enzymatic hydrolysis of crystalline cellulose after pretreatment by NMMO.” Journal of industrial microbiology & biotechnology (2012): 1-10;

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Wiman, Magnus, et al. “Cellulose accessibility determines the rate of enzymatic hydrolysis of steam-pretreated spruce.” Bioresource Technology (2012);

Elliston, Adam, et al. “High concentrations of cellulosic ethanol achieved by fed batch semi simultaneous saccharification and fermentation of waste-paper.” Bioresource Technology (2013);

Kinnarinen, Teemu, et al. “Effect of mixing on enzymatic hydrolysis of cardboard waste: Saccharification yield and subsequent separation of the solid residue using a pressure filter.” Bioresource technology (2012);

Wang, Lei, Richard Templer, and Richard J. Murphy. “High-solids loading enzymatic hydrolysis of waste papers for biofuel production.” Applied Energy (2012);

Li, Sujing, Xiaonan Zhang, and John M. Andresen. “Production of fermentable sugars from enzymatic hydrolysis of pretreated municipal solid waste after autoclave process.” Fuel 92.1 (2012): 84-88;

Dubey, Alok Kumar, et al. “Bioethanol production from waste paper acid pretreated hydrolyzate with xylose fermenting Pichia stipitis.” Carbohydrate Polymers (2012);

Kinnarinen, Teemu, et al. “Solid-liquid separation of hydrolysates obtained from enzymatic hydrolysis of cardboard waste.” Industrial Crops and Products 38 (2012): 72-80;

Nørholm, Nanna Dreyer, Jan Larsen, and Frank Krogh Iversen. “Non-pressurised pretreatment, enzymatic hydrolysis and fermentation of waste fractions.” U.S. patent application Ser. No. 13/405,262;

Das, Arpan, et al. “Production of Cellulolytic Enzymes by Aspergillus fumigatus ABK9 in Wheat Bran-Rice Straw Mixed Substrate and Use of Cocktail Enzymes for Deinking of Waste Office Paper Pulp.” Bioresource technology (2012);

Chen, Hui, et al. “Enzymatic Hydrolysis of Recovered Office Printing Paper with Low Enzyme Dosages to Produce Fermentable Sugars.” Applied biochemistry and biotechnology (2012): 1-16;

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each of which is expressly incorporated herein by reference.

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BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows enzymatic hydrolysis yield of different substrates. Enzyme was added 50 FPU of T. reesei and the hydrolysis was conducted at 50° C. for 3 days.

FIG. 2 shows enzymatic hydrolysis yield of a bleached hardwood kraft pulp (Eucalyptus, Baycel). Different enzyme formulations.

FIG. 3 shows the filler effect on UKP hydrolysis yield. UKP (▪), UKP with 30% of Kaolin (▴), UKP with 30% of CaCO3 (♦) and replication n=2, α=0.05.

FIG. 4 shows hydrolysis yield of UKP and CaCO3 (15%) mixture depending on different Tween-80 dosage with 20 FPU of T. reesei

FIG. 5 shows hydrolysis yield of fines depending on different Tween-80 dosage with 20 FPU of T. reesei.

FIG. 6 shows hydrolysis yield of fines combined diverse dosage of Tween-80

FIG. 7 shows Tween-80 (3%) effect on hydrolysis yield of UKP and mixture material of UKP and fillers. UKP (♦), UKP with Tween-80 (▪), UKP+CaCO3 (15%)+Kaolin (15%) (−), UKP+CaCO3 (15%)+Kaolin (15%) with Tween-80 (•) and replication n=2, α=0.05.

FIG. 8 shows a combination effect of Tween-80 (3%) and low pH buffer for hydrolysis yield. Fines only (▪), Fines with 3% of Tween-80 (▴), Fines with Tween-80 and pH4 buffer (♦) and replication n=2, α=0.05.

FIG. 9 shows a temperature effect on hydrolysis of pure fines and surfactant mixed fines. Fines with Tween-80 (3%) at 50° C. (▴), Fines at 50° C. (▪), Fines at 55° C. (♦), Fines with Tween-80 (3%) at 55° C. (•) and replication n=2, α=0.05.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Material and Methods

Raw Materials

The fines were procured from a NYS based recycled linerboard-manufacturing mill. Additionally a comparative study was undertaken where commercial OCC boxes were repulped and hydrolyzed using commercial cellulases. Unbleached softwood kraft pulp (USKP), an unbleached hardwood kraft pulp (UHKP) and mixtures of fiber and fillers were used for hydrolysis. Recycled OCC was prepared by simple slushing of OCC boxes and dispersion. Pulps were ground and screened through a 200 mesh screen (such that the accepts were less than 75 μm in size).

Samples of commercially available cellulases were obtained—Aspergillus Nigra, and Trichoderma Reesei.

Fines Analysis

pH meter 2500 series of Cole Parmer® was used for evaluating pH of fines and hydrolysate. Solid content and ash content was computed according to the National Renewable Energy Laboratory (NREL) Laboratory Analytical Procedure (LAP, NREL/TP-510-42627, NREL/TP-510-42622). Enzyme activity was also determined by NREL LAP (NREL/TP-510-42628). Particle size and Zeta potential were defined by a particle size analyzer (90 Plus/BI-MAS, Brookhaven Instruments Co.)

Enzymatic Hydrolysis

The hydrolysis of fines was carried in a medium with a solid to liquid ratio of 1:20 with a cellulase dosage of 5-100 FPU using 20 mL sodium acetate buffer. A commercial grade enzyme (C2730, derived from the fungus Trichoderma reesei ATCC 26921) was procured from Sigma Aldrich. The hydrolysis flask was placed in a shaking incubator (Reciprocal Shaking Bath 51221080, Precision Co.,) and hydrolyzed at 50° C. for 72 h at 100 rpm. The solid residue was recovered by filtration with filter paper (Whatman No. 1) and the hydrolysis yield calculated with the weight of sugars divided by total weight of biomass load. Sugar content was analyzed by HPLC.

Filler Effect

To determine effect of filler on hydrolysis yield pulp reject mixtures were generated in the lab composed of unbleached softwood kraft pulp (UKP) mixed with various proportions of Calcium Carbonate and Kaolin. The filler content was varied to understand the influence of each on hydrolysis yield. Imitating the total filler content in original fines, the proportions of calcium carbonate and kaolin were adjusted to a total of 30% (w/w) and the ratio of fillers was varied between 0-30%.

Surfactant Effect

Since fillers provide adsorption surfaces for the cellulase enzymes which are nonproductive in terms of sugar production, one method of inactivation is to shield their surfaces with a suitable surfactant to prevent enzyme adsorption. A cationic and a nonionic surfactant were chosen for this purpose. Cetyl trimethyl ammonium bromide (CTAB, Catalog No. Alfa Aesar, Ward Hill Mass.) was obtained in powder form and stock solutions of 1% w/w in double distilled water were prepared. Similar solutions of a non-ionic surfactant, Tween-80 were also prepared.

Enzyme Hydrolysis Experiments

Samples of the raw material (fines or waste rejects) were preweighed to 1 g dry weight and placed in 100 ml conical flasks provided with magnetic stirrers. Surfactants were also dosed followed by the cellulase mixtures in the required dosages. The flasks were shaken in a water bath for varying times upto 48 h and were removed at different time intervals. The hydrolyzed material was then filtered through 0.1 um filters and the filtrates were taken as the hydrolyzates for yield and compositional analysis by HPLC and 1NMR techniques. The solid residues were dried in an oven and the weights were used in the overall hydrolysis yield calculations. The solid residues were dissolved in 1% sulfuric acid and subsequently filtered again to determine the acid soluble (presumably CaCO₃) contents of the minerals. The remaining insoluble residue was taken to represent Kaolin.

Results

Table 1 shows the characteristics of fines from the waste rejects of a recycled linerboard mill repulping OCC. The solids were obtained from a screw presses at a consistency (oven dry mass of solids/total mass) of 35%, the remainder being water. The average particle size was 2.1 μm. It is likely that the larger particles correspond to fragments of fibers whereas the smaller ones correspond to fillers and other mineral debris in the suspensions. The zeta potential is slightly negative. The higher levels of calcium carbonate and kaolin in the minerals originate most likely from deinking of white paper containing fillers or coated grades of paper. The total ash content was significant consisting 33% (g/g) of fines and Calcium Carbonate (CaCO₃) composed around half of this ash. Lignin was also contained in the fines at 3%. The particle size of fines was around 3 μm and the pH was close to neutral (6.4), but the zeta potential was quite low (−9 mV).

The hydrolysis yields of Avicel, UKP-maple (non-dried), UKP-softwood (dried) and paper mill fines rejects were compared (FIG. 1). Avicel is a microcrystalline cellulose and when subjected to hydrolysis, nearly all of the cellulose was readily converted into monomeric glucose. Similarly, the conversion of the sample of the unbleached kraft (hardwood) pulp was extremely high. This pulp was laboratory prepared (kappa number of 18) and could also be depolymerized to greater than 90%. The softwood pulp sample was converted to yield only 60%, probably due to a larger hemicellulose content. Unbleached kraft softwood pulp shows lower yields primarily because this pulp was dried and reslushed before enzymatic hydrolysis. The process of drying causes the pulps to hornify i.e. limit the accessibility of cellulose by reducing the cell wall porosity. Upon reslushing therefore, a dried pulp fiber will not rehydrate to the same extent as virgin fibers and the cellulases are blocked from entering the crystalline structure to cause hydrolysis. The lowest hydrolysis yield was found for the mill fines rejects; around 0.4 g of sugars from 1 g of fines (OD) among the four substrates.

Fillers inhibit hydrolysis in different ways. One of their primary actions is to competitively bind the cellulases thus rendering a significant fraction of the hydrolytics nonproductive. The effect of such fillers on enzyme hydrolysis is shown in FIG. 2. For this experiment, UKHWP was mixed with 30% of kaolin and CaCO₃ (PCC) in order to make the composition similar to fines and the hydrolysis yield was measured as a function of enzyme dosage (in FPU). The inhibitory effect is different between Kaolin and CaCO₃ and CaCO₃ had a higher inhibitory potential which decreased enzymatic hydrolysis yield.

FIG. 2 shows the glucose yields for two different enzyme mixtures on a sample of bleached kraft hardwood pulp (Eucalyptus). The Trichoderma reesei enzyme was more effective and the Aspergillus niger did not show much activity. Fillers can reduce the yield of sugar simply by their interference with the enzyme action. Most often, their action can be simple competitive adsorption of the enzymes reducing the net activity. The impact of mineral fillers was demonstrated in the present study by mixing kaolin or calcium carbonate filler with unbleached hardwood kraft pulps and subjecting them to hydrolysis. The hydrolysis yield was measured for several enzyme dosages. The results shown in FIG. 3, indicate that calcium carbonate particles have a dramatic impact, reducing hydrolysis yields as compared to kaolin which was minimally active. It appeared that the calcium carbonate fillers could adsorb large amounts of the enzyme.

It may be possible to prevent the interference of hydrolysis by mineral particles by adsorbing a competitive molecule such as a surfactant. Calcium carbonate generally has cationic surfaces whereas charges on kaolin platelets are anionic on the basal surfaces. Kaolin particle edges also show positive charges within a narrow pH range around neutrality. Thus adsorption of ionic or nonionic surfactants could compete and block enzyme adsorption and inactivation by these minerals. We tested the performance of an uncharged (nonionic) surfactant at effecting the hydrolysis. The hydrolysis yield of UKP containing CaCO₃ (15%) was tested with 20 FPU in the range of 0-13% of the nonionic surfactant (Tween-80) dosage. The hydrolysis yield is shown in FIG. 4 as a function of surfactant dosage. The yield increased from 8% to 21% at the surfactant dosage of around 7%. It was observed that the surfactant dosage of lower than 4% and higher than 10% did not have impact for hydrolysis yield increase. Surfactant adsorption on CaCO₃ reaches a maximum at about the 7% level. Further addition results in the surfactant remaining in solution, possibly in micellar form and deactivating the enzymes, resulting in steep reductions in yields as observed beyond an optimal level (9%). FIG. 5 shows the impact of the nonionic surfactant on fines hydrolysis at different enzyme dosages. The yields difference was not significant and even low dosage, 3% of surfactant, obtained slightly higher hydrolysis yield in the range of low FPU.

The surfactant effect in relation to yield increase was measured with the artificial synthetic fines from UKP (softwood) mixture with CaCO₃ and Kaolin. These proportions of fillers in synthetic fines were to imitate the composition of OCC mill rejected fines. The hydrolysis yield of pulp containing fillers was increased with addition of 3% of the Tween-80 (FIG. 6).

FIG. 7 shows the impact of increasing enzyme dosage on the yield for enzymolysis of unbleached kraft pulp samples (at 48 h, taken to be the ultimate or equilibrium value). This figure displays the impact of the CaCO₃ and kaolin fillers, and a possible method of resolving their inhibition using the surfactant. The unbleached kraft pulp hydrolyzes effectively to 60% yields at high enzyme dosages (around 50 FPU). The addition of the surfactant boosts the yields and the enzyme kinetics significantly. When the CaCO₃ and kaolin fillers were included with the UKP (15% and 15%, by weight respectively), the hydrolysis kinetics fell dramatically although the final yield obtained was similar. The inclusion of the surfactant at the optimal dosage resulted in a significant boost to the kinetics and also increased hydrolysis yield.

Besides providing surfaces for competitive and nonproductive i.e. nonhydrolyzing sites for enzyme adsorption, the CaCO₃ could performing as an inhibitor in other important ways. For example, the presence of CaCO₃ alters the pH from the optimal value for hydrolysis and Ca²⁺ ions could interfere in different ways. Charge neutralization and consequent coagulation of particles in the suspensions could occlude enzyme adsorption and thus present kinetic barriers to hydrolysis.

Fine and pH 5 sodium acetate buffer compounds were varied with pH and buffer did not maintain the mixture pH 5 which was the optimal condition for cellulose. Using buffer around pH 5 is common for the enzymatic hydrolysis of cellulosic biomass in order to make the pH of solution stable and proper for enzyme. Addition of the pH 5 buffer to fines changed the pH of solution to around 6.5. The pH 6.5 of the solution was considered as improper initial condition for enzymatic hydrolysis. The buffer of pH 4 was tested and found the initial pH was reduced to 5.5 which was more close to optimal pH condition of the enzyme (pH 5). As the results, the lower pH buffer reinforced ability of enzymatic hydrolysis. Application of proper pH buffer and surfactant was an effective method to increase enzymatic hydrolysis and minimize enzyme dosage (FIG. 8).

The hydrolysis of the cellulosic substrates depends strongly on the accessibility of the internal structure of cellulose, but drying of cellulosic fibers/fines restricts the access to the hydrolytic enzymes (Hornification). Hornification is the result of drying of pulp fibers and fines that results in a loss of amorphous cellulose and reduction of the internal porosity both resulting in marked reduction of the pulp's hydration capacity, which increases pulp crystallinity. The impact of hornification of the fines by drying is quantified in the present study (Table 2). The drying effect i.e. ‘hornification’ seems to be responsible in reducing the cellulolytic yields by nearly 30% for both these substrates.

The presence of print ink can also be an inhibitory factor of enzymatic hydrolysis resulting in the difference between the yields of recycled pulp and virgin pulp. Printed and unprinted OCC were ground to a fine size to determine the decrease in hydrolysis yield. In the results, the gap of enzymatic hydrolysis yields of inked (44% g sugars/g OCC) and non-inked (46% g sugars/g OCC) was not significant.

The hydrolysis yield peaked at 50° C. while further increase in temperature i.e. 55° C., decreased the hydrolysis yield due to degradation of cellulose. At this temperature, even surfactants failed to improve the hydrolysis yield (FIG. 9). At the lower temperature, 40° C., hydrolysis was decreased 15-20% compared to 50° C. (not-shown).

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Claims

1. A method for processing an aqueous stream of fines, comprising:

adding at least one surfactant to the aqueous stream of fines generated through a process of recycling old corrugated containerboards, and the aqueous stream comprises cellulosic fines which are rejected for recycling which have been separated from cellulosic fibers intended for recycling and papermaking fillers comprising calcium carbonate inorganic particles having an affinity for polysaccharide degradative enzymes, the at least one surfactant being added in an effective amount of between 3% to 10% by oven dry weight of the aqueous stream of fines, and the aqueous stream of fines lacks cellulose fibers suitable for papermaking;

adding at least one cellulose degrading enzyme to the aqueous stream of fines, in an amount sufficient to degrade at least a portion of the cellulosic fibers, to form an enzyme, surfactant, and fines-containing solution; and

maintaining the enzyme, surfactant, and fines-containing solution for a sufficient period of time to degrade at least a portion of the cellulosic fibers into fermentable sugars, to achieve at least 10% hydrolysis yield by weight of fermentable sugars per weight of biomass of the fines, having an increased hydrolytic yield with respect to a hydrolysis yield of fermentable sugars per weight of biomass of the fines for the amount of the at least one cellulose degrading enzyme for degrading cellulosic fibers in the aqueous stream of fines in an absence of the at least one surfactant.

2. The method according to claim 1, wherein the aqueous stream of fines is from an old corrugated cardboard recycling facility, and wherein the aqueous stream of fines has 3% lignin by oven dry weight of the aqueous stream of fines.

3. The method according to claim 1, wherein the effective amount of between 3% to 10% is effective to absorb to the calcium carbonate inorganic particles to reduce an affinity of the calcium carbonate inorganic particles for the at least one cellulose degrading enzyme, and below a level which causes agglutination of the aqueous stream of fines.

4. The method according to claim 1, wherein the calcium carbonate inorganic particles comprise precipitated calcium carbonate.

5. The method according to claim 1, wherein the papermaking fillers further comprise kaolin.

6. The method according to claim 1, wherein the at least one polysaccharide degradative enzyme comprises at least one of a cellulase and a hemicellulase.

7. The method according to claim 1, wherein the at least one surfactant comprises polysorbate.

8. The method according to claim 1, wherein the at least one surfactant comprises polysorbate 80.

9. The method according to claim 1, wherein the hydrolysis yield by weight of fermentable sugars per oven dry weight of the cellulosic fibers of the fines is at least 40%.

10. A method for enzymatically hydrolyzing a mixed aqueous stream, comprising:

receiving the mixed aqueous stream which is a waste product from recycling old corrugated containerboards into paper products, the mixed aqueous stream containing cellulosic fines selectively rejected for recycling into paper products separated from cellulosic fibers retained for recycling and papermaking fillers comprising calcium carbonate inorganic particles from the old corrugated containerboards having a binding affinity for hydrolytic enzymes, and the mixed aqueous stream lacks cellulosic fibers suitable for papermaking;

adding at least one surfactant to the mixed aqueous stream in an amount of between 3% and 10% by oven dry weight of the mixed aqueous stream;

adding at least one cellulose hydrolytic enzyme having a binding affinity for the calcium carbonate inorganic particles, and which are inhibited by binding to the calcium carbonate inorganic particles, to the mixed aqueous stream in an amount sufficient to degrade the cellulosic fines, wherein the at least one surfactant in the amount between 3% and 10% is effective to reduce the binding affinity of the at least one cellulose hydrolytic enzyme for the calcium carbonate inorganic particles; and

hydrolyzing the cellulosic fines with the added at least one cellulose hydrolytic enzyme, to achieve a hydrolytic yield of at least 10% sugars per gram oven dry weight of the cellulosic fines, wherein the hydrolytic yield is increased by the addition of the at least one surfactant in the amount of between 3% and 10% as compared to the hydrolytic yield absent addition of the at least one surfactant in the amount of between 3% and 10%.

11. The method according to claim 10, wherein the cellulosic fines comprise 3% lignin by weight of the oven dry weight of the mixed aqueous stream.

12. The method according to claim 10, wherein the amount between 3% and 10% is effective to absorb to the calcium carbonate inorganic particles to reduce an affinity of the calcium carbonate inorganic particles for the at least one cellulose hydrolytic enzyme, and below a level which causes agglutination of the mixed aqueous stream.

13. The method according to claim 10, wherein the calcium carbonate inorganic particles comprise precipitated calcium carbonate.

14. The method according to claim 13, wherein the papermaking fillers further comprise kaolin.

15. The method according to claim 10, wherein the at least one cellulose hydrolytic enzyme comprises at least one of a cellulase and a hemicellulase.

16. The method according to claim 10, wherein the at least one surfactant comprises polysorbate.

17. The method according to claim 10, wherein the at least one surfactant comprises polysorbate 80.

18. The method according to claim 10, wherein the hydrolytic yield by weight of fermentable sugars per oven dry weight of the cellulosic fines is at least 40%.

19. A method for enzymatically hydrolyzing a mixed stream of cellulosic fines and papermaking fillers comprising calcium carbonate-containing inorganic particles, comprising:

receiving the mixed stream of cellulosic fines which is a waste from a recycled paper mill which recycles paper to retain cellulose fibers for papermaking, and the mixed stream of cellulosic fines does not containing cellulose fibers suitable for papermaking, along with the papermaking fillers comprising calcium carbonate-containing inorganic particles from recycling of the paper;

adding at least one surfactant to the mixed stream, in an amount of between 3% and 10% by weight per an oven dry weight of the mixed stream;

adding at least one cellulose hydrolytic enzyme, having a binding affinity for the calcium carbonate-containing inorganic particles, and being competitively inhibited by binding to the calcium carbonate-containing inorganic particles, to the mixed stream;

the amount of the at least one surfactant being sufficient to reduce the binding affinity of the at least one cellulose hydrolytic enzyme for the inorganic particles and the competitive inhibition of the at least one cellulose hydrolytic enzyme by the calcium carbonate-containing inorganic particles, insufficient to inhibit the at least one cellulose hydrolytic enzyme, and insufficient to agglomerate the mixed stream;

adding an acidifier to the mixed stream; and

hydrolyzing the cellulosic fines with the at least one cellulose hydrolytic enzyme at a temperature of 40° C. or higher,

wherein a hydrolytic yield of grams sugars per gram of cellulosic fines of at least 10% is achieved.

20. The method according to claim 19, wherein the at least one surfactant comprises polysorbate 80, the rejected cellulosic fines comprise 3% lignin by weight per an oven dry weight of the mixed stream, and the hydrolytic yield is at least 40%.